1. Field of the Invention
The present invention relates to an electromagnetic clutch suitable for use in a compressor of an automotive air conditioning system.
2. Description of Related Art
An electromagnetic clutch used for a compressor of an automotive air conditioner includes a rotor and an armature. The rotor rotates by receiving a rotational force from a vehicle engine, and the armature is placed to face the rotor with a predetermined slight gap. The armature is connected to a compressor shaft through a hub. In general, there are two types of hub constructions.
In a plate spring type hub construction, one end of the plate spring is connected to an inner hub mounted on the compressor shaft, and another end of the plate spring is connected to the armature.
In a rubber type hub construction, an inner area of a disk-shaped elastic member made of rubber is connected to an inner hub mounted on the compressor shaft, and an outer area is connected to the armature through a cylindrical support plate.
The plate spring type hub construction has no damping mechanism to reduce vibration and torque pulsation from the armature to the hub. Thus, clutch operation noise and torsional resonance of the clutch are not reduced.
In the rubber type hub construction, the resiliency of the elastic member must be sufficient to separate the armature from a friction surface of the rotor when an electromagnet is deenergized. Therefore, the axial dimension of the disk-shaped elastic member must be larger than that of the plate spring arrangement. As a result, the axial dimension of the clutch is enlarged.
JP-U-61-194831 discloses an electromagnetic clutch in which a plate-like elastic member and a rigid plate are provided to position an armature opposite to a rotor. The armature, the plate-like elastic member and the rigid plate are adhesively connected to each other, and the rigid plate is connected to an inner hub through plural plate springs. That is, a collision noise when the armature is coupled to the rotor is reduced by the damping function of the elastic member.
However, in this prior art, the rigid plate supporting the plate-like elastic member is connected to the inner hub by plural separated plate springs, thereby increasing the number of parts and manufacturing cost.